Rubber compositions with improved performance at sub-zero temperatures

ABSTRACT

Hard and semi-hard rubber articles with improved performance at sub-zero temperatures and prepared from rubber compositions characterized by an elastomeric butadiene polymer containing less than about 23 weight percent of bound styrene in the polymer, about 8-25 weight percent sulfur, about 40-70 weight percent of a specific saturated oil the remainder being semi-anthracite coal dust as filler.

United States Patent 1 Chalex et al.

[ June 10, 1975 RUBBER COMPOSITIONS WITH IMPROVED PERFORMANCE AT SUB-ZERO TEMPERATURES [75] Inventors: Paul Chalex; Selwyn R. Mather,

both of Elmhurst, 111.

[73] Assignee: The Richardson Company, Des

Plaines, Ill.

22 Filed: Aug. 24, 1972 21 Appl, No.: 283,599

Related US. Application Data [63] Continuation-in-part of Ser. No. 102,506, Dec. 29,

1970, abandoned, which is a continuation-in-part of Ser. No. 682,518, Nov. 13, 1967, abandoned.

[52] US. Cl 260/33.6 AQ; 136/166; 260/42.32; 260/83.7; 260/94.2 R

[51] Int. Cl. C08c 11/18; C08c 11/22;l-101m 1/02 [58] Field of Search 260/33.6 A0, 41.5, 42.32, 260/83.7, 94.2 R; 136/166 [56] References Cited UNITED STATES PATENTS 2,638,456 5/1953 Laning t. 260/4l.5 R

Chalex et al. 260/33.6 AO Bateman et a1 260/746 OTHER PUBLICATIONS Industrial & Engineering Chemistry, Vol. 47, N0. 5, pps. 1,0771,082, Taft et al.

Primary ExaminerDonald E. Czaja Assistant Examiner-H. H. Fletcher Attorney, Agent, or FirmJohn L. Hutchinson; Alan M. Abrams [57] ABSTRACT 7 Claims, No Drawings RUBBER COMPOSITIONS WITH IMPROVED PERFORMANCE AT SUB-ZERO TEMPERATURES RELATED APPLICATIONS This application is a continuation-in-part of copending application Ser. No. 102,506 filed Dec. 29, 1970 which in turn is a continuation of application Ser. No. 682,518 filed Nov. I3, 1967, both now abandoned.

BACKGROUND OF INVENTION This invention is related to oil-containing rubber compositions having a sulfur content of about 825 weight percent based on the rubber content and which are suitable for preparing semi-hard and hard rubber articles. More particularly, it is related to compositions containing an elastomeric butadiene polymer with less than about 23 weight percent of bound styrene and a saturated oil. These compositions form molded articles which exhibit excellent impact resistance at temperatures in the order of to '40F.

Oil containing rubber compositions which are vulcanizable with sulfur have been used for a wide variety of articles over a considerable period of time. These compositions are primarily characterized by a rubber, an oil which acts as an extender, a plasticizer or lubricant, and sulfur to provide curing of the composition. In most instances, a filler such as coal dust is also present together with various modifiers for particular purposes.

In general, development of these oil-containing rubber compositions has been principally directed to compositions useful for molding into soft rubber articles and those useful for molding into hard rubber articles. In the first, the sulfur level for vulcanization is generally limited to about 4 weight percent based on the rubber present. Illustrative soft rubber articles of commercial interest are tires, industrial belts, and the like.

In the second category, the sulfur level is generally large (above about weight percent) so as to provide sufficient vulcanization for forming hard rubber articles such as combs, bowling balls, and the like.

A more recent development has been rubber compositions with an intermediate sulfur content of about 8-25 weight percent. These compositions have been found useful for molding into semi-hard or hard rubber articles which also exhibit such properties as desirable impact resistance. They have found commercial acceptance as electrical storage battery containers and similar uses where a combination of hardness and impact resistance are important.

In regard to semi-hard and hard rubber articles, it has become increasingly important to improve impact resistance at low temperatures since this property tends to drop off rather significantly as temperatures are reduced below 70 to 80F. Recently, emphasis has been placed on performance at subzero temperatures in the order 20 to 40F. Accordingly, it is important that rubber compositions be developed which exhibit excellent impact resistance at these sub-zero temperature conditions.

SUMMARY Briefly, the invention is directed to rubber composi' tions useful for producing semi-hard and hard molded articles having excellent impact retention at sub-zero temperatures. These compositions are characterized by a sulfur level ofless than about 25 weight percent based on the rubber content, an elastomeric butadiene polymer having a bound styrene content of less than about 23 weight percent, a saturated oil and semi-anthracite coal dust as the filler.

We have found that the utilization of our rubber compositions have produced molded articles with excellent impact retention at sub-zero temperatures of the order of -20 to 40F. Moreover, these compositions have resulted in molded articles with comparable hardness values to thosefor articles previously commercially used such as those illustrated in our prior patent U.S. Pat. No. 3,359,229;

DETAILED DESCRIPTION OF THE INVENTION The rubber compositions of the invention are characterized by an elastomeric butadiene polymer having a bound styrene content of less than about 23 weight percent.

Advantageously, the polymer is characterized primarily by polymeric butadiene units and the defined percentages of bound styrene. It is understood that the styrene content ranges from O to about 23 weight percent, advantageously from about 0 to 15 weight percent and preferably from about 5 to about 10 weight percent, for example a butadiene styrene copolymer having about 5 to about 10 weight percent styrene.

The rubber polymer component is usually present in amount ranging from about 8 to about 20 weight percent and preferably about 8 to about 12 weight percent based on the total composition. In addition, it is usually and advantageously a solid rubber.

The oil component is present in amounts ranging from about 40 to about weight percent based on the rubber polymer or about 3.5 to 7.5 weight percent based on the total composition. While aromatic oils are useful in addition to saturated oils in combination with the defined butadiene polymer, the saturated oils are particularly preferred because of the improved impact performance of the resultant molded articles at subzero temperatures. Those saturated oils particularly preferred are characterized by a maximum of about 8 percent nitrogenbase components and 17 percent first acidaffins and a minimum of about percent of saturates. second acidaffins or mixtures thereof as determined by Rostler-Sternberg analysis, In addition, these oils are furthr characterized byhaving preferably no asphaltenes or a maximum of about 0.5 percent.

The sulfur content of the compositions useful for preparing semi-hard or hard molded articles is usually considered to be within the range of about 1 or 825 weight percent of the rubber component and preferably from about 8 to about 16 weight percent based on the rubber polymer content.

In disclosing further details of the invention, reference will be made to molded rubber-base battery parts, and particularly battery containers which are multi-cell units serving to house the active components of an automotive storage battery. Such containers are specially made by molding compositions comprising of a rubbery elastomer as the principal binder and generally an inert filler such as coal dust. However, it will be understood that the principles of the invention are likewise applicable to all analogous semi-hard or hard rubber articles containing a vulcanizable rubber wherein sulfur is employed within the range of about 825 weight percent based on the rubber content.

As indicated, most hard rubber battery containers are formed from filled rubber compositions. In addition to rubber, oil and sulfur, these compositions comprise primarily an inert filler such as coal dust. In the present EXAMPLE 1 Several rubber compositions were prepared from butadiene rubbers containing by weight approximately 23.5, 18.0, 14.0, 10.0, 5.0 and 0.0 percent styrene and i i the Coal dust.employed however to rflchleye 5 molded into battery containers for impact testing. The the high impact properties at low temperatures 15 sem1 r bber c m t d b ht anthracite. As shown by the following examples bitumiu t I p081 g 3 y 1 3 nous coal as used in our prior U.S. Pat. No. 3,359,229, ma 6 y percen ru percen. Semi-m ram even with low styrene content, will not achieve the decoal dust 1 percent i 8 perwm percent 01] sired impact resistance at low temperatures as achieved 10 E and Very amounts of lubncants' Each with semi-anthracite. Additional components include ormulailon was essentially the same except the accelerators, activators, and the like. Such composi- Change m the Styrene of the rubber whlch was tions are compounded on mills or on a Banbury and are Val-led by i appropnate amounts of a SBR then molded in closed, heated molds to form the ber contammg 23.5 percent styrene with a polybutaditainer into the desired shape and to simultaneously vulene rubber canize the composition to a semi-hard or hard, perma- After preparanon e ach composltwn was molded mm mm state several battery containers which were tested for hardness at ambient temperatures and for impact at approxln forming the compositions contemplated, a preim y and The hardness ferred process suitable for battery containers is dis- 20 testwas measured in terms of a Shore t r. he l d i h patent to Bateman et 1 U P No impact consisted of subjecting the sides of the contain- 2,844 327 I h a process, after i i i l compounders at substantially their mid-height to the impact of a ing, the batch is rapidly comminuted and cooled to re- -P ball pp from Successive heights until move residual heat. Additional milling may then be ema Crack appeared. This test is substantially in accorployed to further disperse the components and improve dance with the procedure described in Browns U.S. homogeneity. The final product, prior to molding, is Pat. No. 2,755,658 and is measured in inches. The test preferably prepared in a powdery or granulated state. results are listed in Table I below.

TABLE I Styrene Content (wt.%) 23.5 18.0 14.0 10.0 5.0 0.0

Hardness Out. 68 6X 67 66 66 66 In. 66 65 64 64 64 64 Bot. 67 67 65 65 65 65 Impact at 77F Range 29-29+ 2949+ 19-29+ 20-29+ 24-29+ 20-29+ Ave. 290+ 290+ 273+ 267+ 265+ 267+ Impact at 0F Range 17-22+ l8-22+ 19 22+ 20-22+ 21-22+ 21-22+ Ave. 202+ 210+ 212+ 215+ 21.8-1- 21.8-1- Impact at 20F Range 5-7 8-10 10-13 11-15 17-19 19-21 Ave. 6.0 9.0 11.5 13.2 17.7 20.0 Impact at F Range 45 5-6 5-8 8-9 10 13 1 3-17 ve. 4.3 5.8 7.3 8.8 12.0 14.8 Impact at -F Range 2-3 4-5 5-8 6-7 7-9 1 O- l 4 Ave. 2.7 4.2 6.0 6.2 8.2 11.7

Battery containers are subjected to considerable As the above data demonstrate, at -20, 30, and movement and jarring during the battery assembly pro- 40F, the differences in performance between the cess and in subsequent transportation, storage and use. compositions become quite evident and demonstrate A c rdingly. in der to avoid cracks and sim ar damthe benefit of reduced styrene content. At each subage, the industry has established certam impact resis- Zero temperature, h i t f th c m ositio with tance requirements. Compliance with the requlrements 0 w i h percent Styrene w i th order f 3-4 15 detel'mlned y sublectmg test Slabs for Selected times that of the value for the composition with 23 .5 tions of a product to lmpact test. such tests mvolve deweight percent styrene, Moreover, the data d terlnmmg the reslstarw? to crac kmg f struck by a strate that the hardness of the compositions with varyfalling ball of predetermined weight whlch 1s permltted ing styrene content Still was very can-[parable to the to drop Q f y f dlstances' Gefleranyt compositions containing larger amounts of styrene. molded articles of this invention are characterized by 7 minimum average impacts at room temperature in the EXAMPLE n Order Of about 4 inches based the impact tests Rubber compositions similar to those of Example I ser e e were prepared with varying sulfur contents of about 8, l0 and l 1 weight percent. In each instance, the rubber The following examples illustrate some of the emwas a SBR polymer with about 10 weight percent stybodiments of this invention. It is to be understood that these are for illustrative purposes only and do not purport to be wholly definitive to conditions or scope.

rene. Battery containers were molded from each composition and tested for hardness and impact resistance with the results listed in Table 11 below.

6 TABLE 11 TABLE III- Continued Styrene (wt.7c) 10.0 10.0 10.0 )i| Sulfur (wt/7r) 11.0 10.0 8.0 St \rc11c ('omcnt Saturated Aromatic Saturated A I mntic Hardness Out. 68 67 65 5 5BR HM w 11.54 23.5 4

In. 66 65 63 Bot. 67 67 65 Impact at 0F Impact at 77F Range 2l-29+ ll-29+ 25-29-1- Range 13-17 10-15 14-21 4-8 Ave. 260+ 263+ 275+ Ave. 14.8 12.5 16.3 6.3 Impact at 0F Range 17-22+ 19-22+ 20-22+ I t a -2()F Ave. 20.3 205+ 211+ 10 Range 10-13 8-10 6-8 2-2 Impact at 20F Range lI-l4 ll-l4 12-16 Ave. 12.0 9.0 6.8 2.0 1 F at 4 16. 1. mpact at 30 angc -l R.

Ave. 10.0 11.0 11. A325 8.5 0 55 i 2 i Impact at 40F Range 7-9 9-10 5-9 impact at 4OOF Ave. 8.0 9.2 7.2 Range 7-8 3-4 3-4 l-2 i5 Ave. 7.2 3.2 3.2 1.5

The results demonstrate that compositions with 5111- The aPOVe results demonstrate the Significantly fur levels of 8-11 weight percent when molded into Proved lmPaet Performance at Sub-Zero temperatures battery containers exhibited very good impact ratings 9 eemposltlons P p from the Saturated at sub zero temperatures and that approximately 10 2O ticularly at 40F, the containers from the saturated oil weight percent sulfur resulted in the best composition Pr ratmgs the r r of twlee those of the at a temperature of -40F. However, in each instance, tamers from the aromatle 0115- the ercent retention of im act based on the avera e p p g EXAMPLE IV for each composition was 30 percent or better compared to the value at 77F, The following tests were conducted to compare the low temperature, impact properties of rubber composi- EXAMPLE iii t1ons containing seml-anthraclte c0al dust w1th compai rable composmons containing b1tum1nous coal dust as Rubber eomposrtrorls were P ep r rrldlvldually the tiller component of such compositions with varying I using a saturated 011 and an aromatlc oil. The saturated l l f styrene f h purpose f h i h diff 011 was further eharaeterlzed a5 havmg Percent of ences between the compositions disclosed in our prior first aeidatfirlsi 37 Percent of Second aerdeffirls and I U.S. Pat. No. 3,359,229 containing bituminous coal percent of nitrogen bases. The aromatic oil was further dust arid those f this present application containing characterized as having 22.0 percent of first acldaffins, ith i l d 48.0 percent Of second acidaffins and 19.4 percent Of Two series of rubber compositions were prepared in nitrogen bases. accordance with the procedures of Example I where For each oil, the styrene content of the rubber was the coal dust filler employed in one series bituminous varied from approximately 10.0 to 23.5 weight percent. and the other series the coal dust employed was semi- Battery containers were molded from these composianthracite. In both series the amount of styrene in the tions and tested for hardness and impact resistance 0 compositions was varied by blending a styrenewith the results listed in Table III below. butadiene copolymer rubber with a polybutadienerubbet. The bituminous coal dust employed in the compo- TABLE In sitions corresponds to the analysis set forth in our prior U.S. Pat. No. 3,359,229 and the semi-anthracite coal 811 C S d A S d A dust had the following analysis:

tyre omem atumte mmdm agi Dry Fixed Carbon Greater than and Less than of SBR 10% 10% 23.5% 23.5% 92 percent 4 V 1a i1 M Hardness OUL 68 69 7] 71 Dry 0 t e atter Greater than 8 and Less than In. 66 67 67-8 70 14 Percent Bo t. 66 68 69 71 5O Nonagglomerating Physical Property lmpac at Z i341 1248 2149+ 1549 The rubber compositions prepared and employed in Ave. 16.8 15.8 255+ 22.2 the test are described in the following Table IV.

TABLE IV TABLE OF COMPOSITIONS Sample No. l 2 3 4 5 6 7 8 9 10 Type of Coal Dust SEMI- ANTHRACITE BITUMINOUS Butadiene-St rene Rubber Component, bs. 331 331 331 331 331 331 331 331 331 331 Styrene in Rubber Component 20 l5 l0 5 0 2O l5 l0 5 0 Coal Dust, Lbs. 2494 2494 2484 2478 2478 2304 2304 2304 2304 2304 Sulphur 36.5 36.5 36.5 36.5 36.5 60 6O 60 6O 60 Process Oil (1) (Shclltlcx 1371) 174 174 184 I 190 206 206 206 206 206 Accelerator (Aliphatic aldehyde Aromatic Amine Condensation Product) 7 7 7 7 7 7 7 7 7 7 Lime 265 265 265 265 265 394 394 394 394 394 Mold Release Agent (Aliphatic Amine) 8 8 8 8 8 8 8 8 8 8 1) ANALYSIS OF OIL: Clay-Gel Analysis:

SSU Viscosity 7: Polar (or Nitrogen Bases) Max. 4.0 at F 500-2000 7r Aromatics 1 (1st Acidaffins) Max. 17.0

70 Aromatics II 2 d A id ffi 30-40 Flash Point F 420 71 Saturatcs 45-65 TABLE V Impact Properties Molded Rubber Compositions Containing Bituminous (Bit) and Semi-Anthracite (S.A.) at Sub-zero Temperatures with Reduced Styrene Content We claim:

1. A molded article having improved impact peformance at sub-zero temperatures, the article being formed by curing in a mold a rubber composition characterized by an elastomeric butadiene polymer having a reduced styrene content of less than about weight percent, the composition containing about 8-20 weight percent of the polymer, and based on the weight of the polymer about 825 weight percent sulfur and about 40-70 weight percent of a saturated oil, and the remainder primarily an inert filler of semi-anthracite coal wherein said oil is characterized by maximums ofabout 8 percent nitrogen base components and 17 percent Sample No. l 2 3 4 5 Weight Styrene in Rubber Com- 20 10 5 0 poncnt Temp. of Type of Impact [Inch-Pounds) Impact F Coal Dust Bit 25.6 25.6 24.6 25.6 20.6 S.A. 11.6 19.0 29.6 26.0

Bit 16.0 5.0 19.6 20.0 14.6 S.A. 4.6 7.6 9.6 14.0 14.0

Bit 8.0 6.0 8.0 9.0 6.6

As may be observed from the data of Table V and from Graphs I and II the impact value of the compositions containing semi-anthracite coal dust are higher at low temperatures than the impact values of the corresponding compositions containing bituminous coal dust as the filler.

It may also be observed particularly from Graphs I and II that as the percent styrene is reduced and especially below about 10 percent the impact value for the bituminous compositions tends to decrease while the impact value of the semi-anthracite actually increases.

It is accordingly apparent that the rubber compositions as disclosed in our prior US. Pat. No. 3,359,518 which contain bituminous coal dust, even with a reduction in styrene below 10 percent, do not have the impact properties of our present rubber compositions of the present applications which contain semi-anthracite as the filler.

While the invention has been described in conjunction with specific examples thereof, these are illustrative only. Accordingly, many alternatives, modifications, and variations will be apparent to those skilled in the art in the light of the foregoing description and it is therefore intended to embrace all such alternatives, modifications, and variations as to fall within the spirit and broad scope of the appended claims.

first acidaffins and a minimum of about percent of saturates, second acidaffins, or mixtures thereof said composition containing an activator comprising lime.

2. The article of claim 1 wherein the polymer is a butadiene styrene copolymer with a styrene content of from about 5 to about 10 weight percent.

3. The article of claim 2 wherein the sulfur is present within the range of from about 8 to about 16 weight percent based upon the polymer.

4. A multicell battery container having a hardness at least comparable to semi-hard rubber compositions and further characterized by improved impact performance at sub-zero temperatures, the container being molded from the composition of claim 1.

5. The container of claim 4 wherein the polymer of the rubber composition is composed primarily of polymeric butadiene units and has a styrene content in the amount of from about 5 to 10 weight percent.

6. The container of claim 5 wherein the rubber composition contains sulfur within the range of from about 8 to about 16 weight percent based upon the polymer.

7. The container of claim 4 wherein the rubber composition has a sulfur content of about 8 to about 16 weight percent and the polymer contains from about 5 to about 10 weight percent styrene.

l l =l l 

1. A MOLDED ARTICLE HAVING IMPROVED IMPACT PERFOMANCE AT SUB-ZERO TEMPERATURES, THE ARTICLE BEING FORMED BY CURING IN A MOLD A RUBBER COMPOSITION CHARACTERIZED BY AN ELASTOMERIC BUTADIENE POLYMER HAVING A REDUCED STYRENE CONTENT OF LESS THAN ABOUT 10 WEIGHT PERCENT, THE COMPSITION CONTACTAININH ABOUT 8-20 WEIGHT PERCENT OF THE POLYMER, AND BASED ON THE WEIGHT OF THE POLYMER ABOUT 8-25 WEIGHT PERCENT SULFUR AND ABOUT 40-70 WEIGHT PERCENT SATURATED OIL, AND THE REMAINDER PRIMARILY AN INERT FILLER OF SEMI-ANTHRACITE COAL WHEREIN SAID OIL IS CHARACTERIZED BY MAXIMUMS OF ABOUT 8 PERCENT NITROGEN BASE COMPONENTS ABH 17 PERCENT FIRST ACIDAFFINS AND A MINIMUM OF ABOUT 75 OERCENT OF SATURATES, SECOND ACIDAFFINS, OR MIXTURES THEREOF SAID COMPOSITION CONTAINING AN ACTIVATOR COMPRISING LIME.
 2. The article of claim 1 wherein the polymer is a butadiene styrene copolymer with a styrene content of from about 5 to about 10 weight percent.
 3. The article of claim 2 wherein the sulfur is present within the range of from about 8 to about 16 weight percent based upon the polymer.
 4. A multicell battery container having a hardness at least comparable to semi-hard rubber compositions and further characterized by improved impact performance at sub-zero temperatures, the container being molded from the composition of claim
 1. 5. The container of claim 4 wherein the polymer of the rubber composition is composed primarily of polymeric butadiene units and has a styrene content in the amount of from about 5 to 10 weight percent.
 6. The container of claim 5 wherein the rubber composition contains sulfur within the range of from about 8 to about 16 weight percent based upon the polymer.
 7. The container of claim 4 wherein the rubber composition has a sulfur content of about 8 to about 16 weight percent and the polymer contains from about 5 to about 10 weight percent styrene. 